Getting Younger Every Year

Over four years ago, JASON (the group of independent scientists that advises the government on security and other technical issues) completed a report on “Pit Lifetime,” which discusses the aging of the plutonium pits that are part of the primary stage of every U.S. nuclear weapon. (It was publicly released early the following year.)

You may recall that aging plutonium was the first rationale for the Reliable Replacement Warhead (RRW) Program. Plutonium only exists naturally in trace amounts and is made in nuclear reactors. Since plutonium was first created during World War II, no one really knew how it would behave in the future as it continued to age. It was possible that the plutonium would degrade in a way that would have a negative effect on weapon performance.

So there was legitimate cause for concern. The working assumption on the part of the weapons laboratories was that the effective “lifetime” of plutonium was 45 to 60 years.

Meanwhile, some folks at the weapons labs were quite sensibly doing experiments to learn more about plutonium aging. They were able to artificially speed up plutonium aging so that one year in real time corresponded to 16 years in plutonium time. The authors of the JASON report reviewed the data and conclusions from these experiments. Their report endorsed the labs’ work, stating:

Most primary types have credible minimum lifetimes in excess of 100 years as regards aging of plutonium; those with assessed minimum lifetimes of 100 years or less have clear mitigation paths that are proposed and/or being implemented.

The problem of plutonium aging was not much discussed by the National Nuclear Security Administration (NNSA) after that. Instead, talk turned to the purported problems that would result if weapons underwent successive life-extension programs (which JASON dismissed in another report, but that’s another story).

The plutonium aging experiments are, quite sensibly, continuing and each year the samples age another 16 years. Four years later, we’re up to 164 years old! I don’t know the results, but I suspect no news is good news. If the experiments had resulted in plutonium degradation, we would surely have heard about it.

With every passing year, the plutonium lifetime increases and the plutonium in U.S. weapons just keeps getting younger and younger.

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Lisbeth Gronlund is a physicist and co-director of the Global Security Program. She is an expert on technical issues related to U.S. nuclear weapons policy, and new nuclear weapons, space weapons, and ballistic missile defenses.